Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems (2012)

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6Literature Review At the outset of the project a detailed literature review was performed to gather information related to cable barriers with a focus on the design, performance, evaluation, maintenance, and application of cable barrier systems. Many types of documents were collected, organized, and reviewed including cable barrier research papers and reports, presentations, DOT guidelines, in-service evaluations, international studies, usage and safety performance statistics, and success stories. A synthesis of the collected information is presented in the following sections and the documents are available at http://crash.ncac.gwu.edu/dmarzoug/CableBarrierLiterature/. 2.1 History and Usage Cable barriers have been used in the United States for more than 60 years. New York DOT played an important role in the development and refinement of the cable barrier. Early use of cable barriers was concentrated in the northern states because of the openness of the barrier, which allows snow to pass through rather than pile up in front of the barrier as is the case with beam and concrete barriers. A 1982 study by Post and Chastain showed that cable guardrails were more cost-effective than (strong-post) W-beam guardrails for certain types of installations [1]. In 1997, it was reported that 18 states had 3-cable low-tension barriers in use; however, only 4 states were still installing cable barriers [2]. Until 2000, all cable barriers in the United States were low-tension, non-proprietary systems. In 2000, the first high-tension proprietary cable barrier system was installed in Oklahoma City, OK. A safety barrier, developed by Brifen in the United Kingdom in the 1980s and used in over 30 countries, was installed first on an experimental basis on a 305 m (1,000 ft) section of the Lake Hefner Parkway in Oklahoma City in August 2000. Shortly thereafter it was installed along 11 km (7 miles) of the parkway. The Brifen system performed well, which led other states and other manufacturers to get interested in high-tension cable barriers. Since 2000, the use of high-tension cable barriers has expanded rapidly in the United States. Table 2.1 shows cable median barrier usage in the United States for 1997, 2004, and 2006 as reported by Ray in a report for Washington State DOT [3]. This table is based on several surveys of state DOTs, and it is not believed to give a complete picture of usage. For example, Oklahoma, which started the movement toward high-tension cable barriers, is not shown as a user of median barriers in the 2004 surveys even though it had been using cable barriers since 2000. Several states shown to be using cable barriers in 2004 are not included in the 2006 survey. From 2000, when Oklahoma installed its experimental section of Brifen cable median barriers, usage of high-tension cable barriers had spread to at least 30 states by 2006. Table 2.2 gives Ray’s estimate of the number of miles of cable median barrier in use at the end of 2006 by state in the United States. C h a p t e r 2

Literature review 7 Table 2.3 gives an estimate of installed miles of cable barrier for four different points in time, April 2006, September 2006, January 2008, and April 2008. These data gathered by the Texas Transportation Institute (TTI) show the rapid rate of installation of high-tension proprietary cable barriers that has occurred since 2006. Between September 2006 and April 2008, over 1,000 miles of cable barrier were installed. The growth in use of high-tension cable barriers from 7 miles in 2001 to almost 2,700 miles in 2008 is remarkable. Also, it should be noted that the TTI numbers do not consider low-tension, non-proprietary cable barriers. The difference between Ray’s estimate of 2,600 miles at the end of 2006 and TTI’s estimate of 1,645 miles can be explained in large part by TTI’s exclusion of low-tension barriers. For example, North Carolina is reported by Ray to have 600 miles of barriers installed, and most of these miles were low-tension barriers. 2.2 Cable Barrier Designs Cable barriers are categorized as weak-post barriers since their posts are designed to fail in a crash to allow the longitudinal structural element (cable) to absorb energy from the impact through elongation (stretching). The elongation of the cable causes the barrier to deflect laterally in a parabolic form that assists in redirecting the impacting vehicle in a smooth and “forgiving” manner. The elastic nature of the barrier reduces the severity of the impact but causes larger dynamic deflections than would be experienced with a semi-rigid or rigid barrier under similar Year No. States Reporting Cable Median Barrier Use 1997 4 North Carolina, Washington, South Dakota, Missouri 2004 12 Alabama, Arizona, Iowa, Mississippi, Missouri, Nebraska, Nevada, New York, North Carolina, South Carolina, Washington, Wisconsin 2004 14 Alabama, Arizona, Iowa, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Jersey, New York, North Carolina, South Carolina, Washington, Wisconsin 2006 25 Alabama, Arkansas, Arizona, Colorado, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Maine, Missouri, Montana, Nevada, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Texas, Utah, Virginia, Washington, Wisconsin Table 2.1. States using cable median barriers [3]. State Miles Year State Miles Year State Miles Year Alabama 118 2006 Maine 1.5 2006 Oregon 23 2005 Arizona 89 2006 Minnesota 6.3 2003 Rhode Island 1.4 2005 Colorado 40 2005 Missouri 250 2006 S. Carolina 470 2005 Florida 187 2005 N. Carolina 600 2007 Texas 500 2006 Iowa 64 2007 New York 5 1989 Utah 16.4 2003 Illinois 70 2005 Ohio 27.5 2006 Washington 135 2006 Kentucky 13 2006 Oklahoma 23 2005 Total 2,640 Table 2.2. Cable median barrier mileage estimate [3]. Manufacturer April 2006 September 2006 January 2008 April 2008 Safence 4 17 110 185 Brifen 287 323 405 440 Gibraltar 195 395 540 685 Nucor Steel Marion 221 340 403 453 Trinity Industries 341 570 825 912 Total Miles Installed 1,048 1,645 2,283 2,675 Table 2.3. Approximate miles of installed high-tension cable barriers [4].

8 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems impact conditions. Thus weak-post barriers can be used safely only when adequate clear area exists behind the barrier to accommodate the dynamic deflection. The development of weak-post barriers is described in a 1967 publication by Graham et al. [5]. The article describes the theory behind weak-post barriers as well as crash tests conducted on the standard 3-cable barrier, the weak-post W-beam guardrail, and the box-beam median barrier. A summary of available cable barrier systems is presented in Chapter 4 of this report. 2.3 Performance of Cable Barriers Low-tension cable barrier systems have been in use for at least 60 years, and their performance has been studied extensively. Many of the earliest studies were done in New York because New York DOT was the main developer of the 3-cable low-tension barrier. Gabler et al. describe these early studies and later studies of 3-cable low-tension barrier performance. Findings of these studies are summarized in Table 2.4, and more details on these studies are provided in Gabler’s Evaluation of Cross Median Crashes [6]. North Carolina has been the leading user of low-tension cable barriers, having 966 km (600 miles) installed as of 2007 [3]. In 1998, North Carolina began a program to prevent and reduce the severity of cross-median crashes. The program is being carried out in the following three phases: Phase I: Add median protection to freeways with historical crash problems; Phase II: Systematically protect all freeways with median widths of 21 m (70 ft) or less; and Phase III: Revise design policy to protect future freeways with median widths of 21 m (70 ft). Between 2000 and 2006 in North Carolina, approximately 1,600 km (1,000 miles) of freeways were enhanced at a cost of over $120 million. The number of crossover fatal crashes decreased from 33 crashes in 1998 to 4 crashes in 2005 (from 16.7 percent of all fatal crashes to 2.8 percent). Similarly, the number of cross-median fatalities was reduced from 47 fatalities in 1998 to 6 fatalities in 2005 (from 20.5 percent of all fatalities to 3.6 percent). It is estimated that 110 fatal cross-median crashes have been avoided and 177 lives saved from January 1999 to September 2006, resulting in crash cost savings of more than $385 million in fatal crash cost alone (using 2001 dollars). Table 2.5 shows North Carolina’s fatal crash data for 1990 to 2006 [7]. A long-term median barrier evaluation in North Carolina investigated 689 km (428 miles) of new median barrier installations (203 miles of low-tension cable barrier, 132 miles of W-beam State Researchers Date No. of Crashes Findings NY Van Zweden, Bryden 1967- 196 9 375 RS 20% penetrations, 4 fatalities, 15 injuries, 356 no injuries NY Carlson, Allison, Bryden 1977 23 RS (12 LON, 11 term) 33% penetrations, 2 minor injuries, 21 no injuries IA Schneider 1979 31 RS 23% penetrations, 1 fatality, 4 injuries NY Tyrell, Bryden 1989 99 Median 4% penetrations, 24 injuries, 75 PDO NY Hiss, Bryden 1992 427 RS 20% penetrations, 38 major injuries, 178 minor injuries, 211 PDO NY Hiss, Bryden 1992 16 Median 6% penetrations, 1 major injury, 10 minor injuries, 5 PDO NC Mustafa 1997 125 Median 11 major injuries, 28 minor injuries, 88 PDO OR Sposito, Johnson 1999 53 Median 6% penetrations, 5 major injuries WA McClanahan, Albin, Milton 2004 59 Median per year No fatalities, 10 penetrations, 5 heavy vehicle containments RS – Roadside, PDO – Property Damage Only Table 2.4. Previous studies of performance of low-tension, 3-cable barriers [6].

Literature review 9 guardrail, 43 miles of W-beam/cable mix, 31 miles of weak post W-beam, and 18 miles of W-beam/weak post W-beam mix). An analysis of before and after crash data showed that the added median barriers reduced fatal and severe injury crashes and cross-median crashes. For freeways with cable barriers, fatal and severe injury crashes overall were reduced 13 percent while fatal and severe injury cross-median crashes were reduced 74 percent. The data also showed that the added median barriers increased the number of total crashes, the number of minor injury crashes, and the number of property-damage-only crashes. For freeways with cable barriers, the total number of crashes increased 113 percent from 793 to 1,688. Of the 895 additional crashes, only 568 (63 percent) were crashes involving the median barrier. The other 37 percent of the additional crashes may have been a result of the 34 percent increase in ADT between the before period and the after period. The summary data are presented in Table 2.6 [7]. The other state that has installed a lot of low-tension cable barriers is Missouri. As part of Missouri’s Blueprint for Safer Roads Program, approximately 800 km (500 miles) of cable barrier, both low- and high-tension, had been installed as of 2007. These cable barriers have been found to be about 95 percent effective in preventing vehicles from entering opposing lanes. Figure 2.1 shows that statewide cross-median fatalities have dropped from an average of about 50 per year to fewer than 10 per year after installation of the cable median barriers [8]. Figure 2.2 shows the relationship between the installation of cable barriers and the reduction in cross-median fatalities on I-70 in Missouri. In 2003, when Missouri began its major program to install median barriers, I-70 had 23 fatalities from cross-median crashes. In 2007, when Missouri had in place 290 km (180 miles) of median barrier on I-70, fatalities from cross-median crashes had dropped 83 percent to 4 cross-median fatalities [8]. In 2006, Missouri used accident data from 1999 to 2005 to evaluate the performance of its low-tension cable barrier on medians with slopes steeper than 6H:1V. Many of these slopes were 5H:1V, but some were steeper. Of the 1,402 accidents investigated, 67 (5 percent) were marked as a “failure,” meaning that a crossover was not prevented [1]. In 2004, Washington DOT studied the in-service performance of its low-tension cable barriers. Before and after accident data showed that the average number of crashes per year increased from Median Barrier Projects Started Here Table 2.5. North Carolina fatal crashes from 1990 to 2006 [7].

10 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems 49 to 100; however, the average annual rate of fatal crashes dropped 89 percent from 3.00 to 0.33. Likewise, the average annual rate of disabling crashes dropped 51 percent from 3.60 to 1.76. Washington DOT estimates that the societal costs due to such crashes were reduced 76 percent from $13.58 million to $3.32 million [1]. Ray has summarized the data from several states on reductions in cross-median crashes [3]. These data (shown in Table 2.7) are for installations of both low- and high-tension cable barrier systems. Some of the data is based on small sample sizes, which implies that some of the results Table 2.6. Median barrier before and after crash data at select locations in North Carolina [7]. 2002 2003 2004 2005 2006 2007 48 52 0 20 40 60 40 50 26 9 Fa ta lit ie s Figure 2.1. Missouri interstate cross-median fatalities [8].

Literature review 11 shown have wide statistical confidence intervals. Table 2.8 shows the effectiveness of cable barriers in preventing cross-median penetrations. All but one state reported 93 percent effectiveness or better. Utah’s 88.9 percent effectiveness is based on only 18 crashes. The two states reporting 100 percent effectiveness, Iowa and Rhode Island, also are based on small sample sizes. From these data, the average effectiveness of cable barriers in preventing median barrier penetrations (including or excluding the three states with small sample sizes) is 98.0 percent [3]. A number of states have performed in-service evaluations of high-tension cable barriers since these systems were new to the DOTs. Summaries of these studies are given in Table 2.9. All reports indicate that the high-tension cable barrier systems are effective in reducing cross-median crashes. Figure 2.2. Cable installations vs. cross median fatalities—I-70 in Missouri [8]. State Annual “Before” Annual “After” Reduction (Number) (Number) ( percent) Fatal Cross-Median Crashes Alabama 47.5 27 43 Arizona 1.7 0.7 59 Missouri 24 2 92 North Carolina 2.1 0 100 Ohio 40 0 100 Oklahoma 0.5 0 100 Oregon 0.6 0 100 Texas 30 1 97 Utah 15 0 100 Washington 4.4 0.4 91 Cross-Median Crashes Florida --- --- 70 North Carolina 25.4 1 96 Ohio 371 27.5 93 Utah 114 55 52 Washington 42.4 11.2 74 Table 2.7. Performance of cable median barriers in various states: reduction in cross-median crashes [3].

12 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems 2.4 Placement of Barriers The TTI report entitled “Guidelines for the Selection of Cable Barrier Systems (Generic Design vs. High Tension)” discusses the tradeoffs involved in the lateral placement of cable barriers. To reduce the number of impacts, the barriers should be placed as far away from the travel lane as possible. To achieve the highest level of performance, the barrier should be placed on near-level terrain, which usually is found close to the travel lanes. Also, adequate clear space behind the barrier must be maintained to allow for dynamic deflection of the barrier during impacts [1]. Cable barriers are typically placed on medians with slopes of 6H:1V or flatter. However, several of the high-tension barrier systems have been crash-tested successfully on 4H:1V median slopes. To reduce the chance of barrier penetration from reverse hits on medians with 6H:1V slopes, barriers should not be placed from 1 ft to 8 ft from the ditch centerline [1, 17]. Barriers placed along the centerline of median ditches have experienced problems from poor and saturated soil conditions and drainage inlets. The poor soil conditions can cause foundation and anchor failures, and the drainage inlets have been found to allow vehicles to penetrate the barrier because of the increased height of the cables at the inlet. State Collisions (Number) Penetrations (Number) Effectiveness ( percent) Arkansas 490 25 94.9 Louisiana 20 0 100 North Carolina 71 5 93.0 New York 99 4 96.0 Ohio 372 4 98.9 Oklahoma 400 1 99.8 Oregon 53 3 94.3 Rhode Island 22 0 100 South Carolina 2,500 10 99.6 Utah 18 2 88.9 Washington 774 41 94.7 Table 2.8. Performance of cable median barriers in various states: effectiveness [3]. State System Miles Time Crashes Fatal Serious Injury Minor Injury Heavy Vehicle Pene- tration Ref AR Brifen 1 yr 44 0 0 0 1 0 [9] AZ Brifen 40 30 mo 104 1a 0 4 8 0 [10] CO Brifen 2.3 18 mo 9 0 0 0 1b [11] IN Brifen 13 1 yr 70 0 0 0 1 4c [12] IO Brifen 3.5 21 mo 20 0 1d 0 0 0 [13] OH Brifen 14.5 3 yr 452 0 0 39 13 [14] OK Brifen 7 1 yr 128 0 0 1 0 [15] RI CASS 1.4 1 yr 20 0 0 0 0 [3] TX Brifen 13 mo 65 [16]TX Nucor 6 mo 6 TX CASS 13 mo 76 UT CASS 8 16 mo 74 0 2 3 [1] UT Brifen 2 18 mo 11 0 1 3 a Fatality unrelated to barrier, b penetration occurred at a drainage inlet where the cables were higher than specified, c no cross-median crashes, d injury occurred during impact with tractor-trailer before impact with barrier. Table 2.9. Performance of high-tension cable barriers in various states.

Literature review 13 Ray’s cable barrier summary [3] contains a table with data from ten states on their guidelines for installing cable median barriers. His table has been reproduced as Table 2.10. The most common recommendations are “center of median” and/or “greater than 8 ft from the bottom of the ditch,” which is consistent with the TTI report and the AASHTO Roadside Design Guide. Missouri recommends for medians at least 9 m (30 ft) wide, to place the cable barrier 1.22 m (4 ft) down slope of the edge of median (hinge point). For medians narrower than 9 m (30 ft), the cable barrier should be installed at the vertex of the V or flat-bottomed ditch [18]. FHWA-sponsored research at the National Crash Analysis Center of the George Washington University has investigated the issue of median crossovers by conducting full-scale crash tests of a large sedan impacting a cable barrier placed at a 1.22 m (4 ft) offset from the center of V-shaped 6H:1V sloped median [19]. In addition, vehicle dynamics simulations were used to evaluate and optimize cable barrier performance on sloped medians under different impact conditions. Vehicle dynamics simulations were conducted to compute vehicle trajectories as they cross or traverse a median on a diagonal path. A commercially available software package was used to undertake the computations and generate an animation showing what happens. In these studies, the vehicle trajectory as it crosses the sloped median was computed and used to determine if the barrier would engage and redirect the vehicle. Simulations with varied vehicle types (small car, large sedan, and pickup truck), impact speeds (50 to 100 km/h, 31 to 62 mph), approach angles (5 to 25 degrees), median profiles (V-shaped and flat bottom), median slope (8H:1V, 6H:1V, and 4H:1V), and median widths (5 to 17 m, 16 to 56 ft), were conducted to assess barrier performance. The vehicle’s relative height was compared to vertical locations of the cables to assess vehicle-to-barrier interaction. The analysis was used to investigate individual cases (i.e., one vehicle, one speed, one angle, and one median profile) as shown in Figure 2.3. The figure shows a trace envelope for the vehicle moving left to right relative to the cross-section of the median and six possible placement locations for this 3-cable barrier design. Interface with all cables is clearly good (Good oval) and missing all cables is bad (Bad oval). Interfacing with only one or two of the cables is considered acceptable. Table 2.10. Cable barrier installation guidelines [3].

14 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems Test 1 Placement Test 2 Placement GOOD BAD 3 feet Vehicle Direction Figure 2.3. Sample trace envelope of vehicle crossing a sloped median. Additionally, trace envelopes from several cases (varied vehicle types, speeds, and angles) were combined to study optimum placement of cable barriers. Figure 2.4 shows sample plots highlighting a region in the median between 1 ft and 8 ft where significant variations in vehicle vertical position are observed. Similar variation for this critical region was noticed for different median widths (5 to 15 m, 16 to 48 ft), as indicated by the pattern of “bulges.” This plot indicates that barrier placement in this region should be avoided or additional cables are needed [19]. 2.5 Cable Heights Cable heights are important in determining cable barrier effectiveness. Existing cable barriers have either three or four cables (19 mm, ¾ in, 3 × 7 strand galvanized wire ropes). Most high-tension cable barriers use prestretched cables to reduce post-construction tension loss caused by construction stretch (the seating of wire strands during loading). Although cable heights vary among barrier systems, in most systems, the bottom cable is between 432 and 533 mm (17 and 21 in.) high. The top cable height for most systems is between 762 and 1,067 mm (30 and 42 in.). Figure 2.5 shows cable heights for some of the available cable barrier systems. A more complete list of available systems and their cable heights is included in Appendix B of the contractors’ final report. Cable barriers need to accommodate a wide range of vehicle types, from low-profile sports cars to high-center-of-gravity trucks. If the bottom cable is too high, then low-profile vehicles can potentially penetrate under the cables. If the top cable is too low, large vehicles can potentially override the barrier. If the cables are too far apart, vehicles could penetrate between the cables. The 4-cable systems provide for a wider coverage of vehicles (such as TL4 vehicles) than do 3-cable systems, but they are marginally more expensive because of the additional cable. The cable heights for existing barriers work well for impacts on level terrain. However, these heights may not work well when cable barriers are placed on slopes and optimum lateral placement becomes critical to ensure adequate performance.

Literature review 15 16 ft Median 24 ft Median 32 ft Median 40 ft Median 48 ft Median Figure 2.4. Vehicle trajectories from computer simulations of a pickup truck traversing a V-shaped 6:1 sloped median at different impact speeds and angles [19]. Figure 2.5. Sample cable barrier design variations [19].

16 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems 2.6 Deflection, Post Spacing, and Anchor Spacing The dynamic deflection of a cable barrier during impact is an important characteristic for many reasons. Compared to semi-rigid W-beam barriers and rigid concrete barriers, cable barriers have much greater deflections, which is the reason that cable barriers typically are more forgiving to the impacting vehicle’s occupants. However, for the barrier to be safe, adequate space behind the barrier that is clear of hazards must be provided. If deflections are too large, the impacting vehicle could crash into rigid objects behind the barrier or worse yet, collide with a vehicle in the opposing lane of traffic on a divided highway. The dynamic deflection in a particular crash depends on many factors including impact conditions (vehicle speed, impact angle, and mass), barrier design (post spacing, post cross- section, post foundation/embedment, anchor spacing, cable-post interface/connection, number of cables restraining the vehicle, cable tension, cable modulus of elasticity), and environmental conditions (coefficient of friction of ground, soil strength, terrain slope). Because of these many factors, it is not possible to predict exact deflections that will occur in the field. Cable barriers were crash-tested according to guidelines contained in NCHRP Report 350 [20]. Systems developed after 15 October 2009 must be tested according to the procedures described in the Manual for Assessing Safety Hardware (MASH) [21]. One of the reported outcomes of crash tests is the maximum dynamic deflection that occurred during the test. Since the NCHRP Report 350 crash tests are conducted under standardized conditions, the reported dynamic deflection may provide a basis for comparing different barrier system designs if similar installation length, post spacing, and initial tension are used. The dynamic deflection, which occurs in the field under conditions that differ from the standard test conditions, will be different from the deflection reported during the crash test. An FHWA memorandum dated 20 July 2007, and sent to FHWA division administrators, provided detailed information on a number of cable barrier considerations [22], as follows: • In general, deflection distance is known to increase with longer spacing between posts. • What is not known, but strongly suspected, is that longer post spacing may also affect the propensity for vehicles to penetrate the cable barrier, i.e., by underride or by traveling between cables. • The FHWA recommends that the highway agencies specify the post spacing when cable barriers are bid. The conventional range for cable post spacing is 2 to 4.6 m (6.5 to 15 ft). • Prestretched cables have advantages including reduced dynamic deflection by reducing the “play” between the individual wire strands in the bundle that forms the cable prior to installation. • The “design deflection” noted in each FHWA acceptance letter is the minimum deflection distance that should be provided to fixed object hazards and is based on NCHRP Report 350 Test 3-11 using the 2000P (2,000 kg, 4,400 lb) pickup truck. • The deflection distance recorded in FHWA letters is also related to the length of the test installation. For example, if a 91 m (300 ft) long barrier is tested and the “design deflection” recorded, the actual deflection under similar conditions will be greater if the barrier length between tie-downs exceeds 91 m (300 ft). Future crash test criteria will specify a minimum installation length for test sections on the order of 183 m (600 ft) to better determine the deflection that can normally be expected. The National Crash Analysis Center (NCAC) at George Washington University performed a number of simulations on two different types of cable barrier systems for two different initial cable tensions and for three different anchor spacings [23]. Finite element models of an interwoven

Literature review 17 (weaved) 4-cable barrier and a non-woven (parallel) 4-cable barrier were developed and validated. Post spacings were 3.2 m (10.5 ft) for the weaved system and 3.0 m (10 ft) for the parallel system. Two cable tensions, 15 kN (3.2 kips) and 24 kN (5.2 kips), were used for the initial tension in the system before impact. These tensions approximately represent typical “hot weather” (100°F) and “average weather” (50°F) conditions respectively for high-tension cable barriers. Anchor spacings of 100 m to 1,000 m (3,300 ft) were used in the simulations. The 100 m (330 ft) length is the typical spacing used for NCHRP Report 350 crash tests. The results of the simulations are shown in Figure 2.6. As expected, the deflections increase for lower cable tensions. The very small change (<5 percent) in deflection for the 38 percent decrease in cable tension is explained by the very large change in cable tension that occurs during an impact. Increases in cable tensions at the anchors during impact are 4 to 5 times as large as the before-impact tension. This finding indicates that for high-tension cable barriers, dynamic deflections from crashes occurring during hot weather when cable tensions are lower should not be much greater than what would occur during average weather. Anchor spacing was found to have a significant impact on deflection. For both systems, parallel and weaved, the increase in deflection resulting from an increase in anchor spacing from 100 m (330 ft) to 300 m (990 ft) was about 25 percent. However, for anchor spacings greater than 300 m (990 ft), the two systems behave differently. The simulations indicate that the weaved system reaches a maximum deflection at an anchor spacing of approximately 300 m (990 ft), and for anchor spacings greater than 300 m (990 ft) the deflection remains constant. This phenomenon is explained by the very high frictional force exerted on the posts by the interwoven cables, which causes each post to act somewhat like a mini-anchor. With non-woven parallel cable systems, the frictional force exerted on the posts is low, and deflection continues to increase with larger anchor 5 6 7 8 9 10 11 0 500 1000 1500 2000 2500 3000 3500 4000 1.5 2.0 2.5 3.0 3.5 0 200 400 600 800 1000 1200 End-anchor Spacing (ft) B ar rie r D ef le ct io n (m ) B ar rie r D ef le ct io n (ft ) End-anchor Spacing (m) Weaved System - 24 kN (5400 lb) Tension - 3.2 m (10.5 ft ) Post Spacing Weaved System - 15 kN (3400 lb) Tension - 3.2 m (10.5 ft ) Post Spacing Parallel System - 24 kN (5400 lb) Tension - 3 m (9.8 ft ) Post Spacing Parallel System - 15 kN (3400 lb) Tension - 3 m (9.8 ft ) Post Spacing Figure 2.6. Effects of pre-impact cable tension and anchor spacing on deflection [23].

18 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems spacings. Simulations were not conducted on anchor spacings longer than 1,000 m (3,300 ft) because of the very long computation time required. Also, simulations were not conducted on other post spacings to determine the impact of post spacing on deflection. These findings are very important, since some highway agencies expect that the deflections reported with crash tests will be what will occur in the field. 2.7 Horizontal Curves Horizontal curves affect cable barrier performance and must be considered when deciding where to place the cable barriers. Tension in the cables is what allows cable barriers to redirect vehicles. Impacts on the concave side of a curved cable barrier are not a problem; however, impacts on the convex side of a curved cable barrier will result in significantly higher deflections because of the slackening of the cables that occurs. The increase in deflection is a function of the sharpness of the curve and the anchor separation. Alberson et al. determined deflection magnification factors by using Barrier7 software to conduct a parametric analysis of concave impacts [1, page 46]. This study examined low-tension cable barriers with a 5 m (16 ft) post spacing using as the base a 90 m (295 ft) anchor spacing and a straight section. The analysis gives magnification factors of 1.39 for a 4° curve with 90 m (295 ft) anchor spacing, 1.19 for a 0° curve (straight section) with 450 m (1,500 ft) anchor spacing, and 2.54 for a 4° curve with 450 m (1,500 ft) anchor spacing. These values are not applicable to high-tension cable barriers. Since roadside encroachments are more common on the outside of a curve, TTI recommends that median cable barriers on horizontal curves be placed on the far side of the centerline ditch away from the outside of the highway curve. Placing the barrier farther away from the more likely encroachment provides more space for the driver to avoid the barrier, and any errant vehicles that hit the barrier will hit it on the concave side. However, this positioning puts the barrier closer to the opposing lanes where an encroaching vehicle will hit the barrier on the more vulnerable convex side [1]. 2.8 Maintenance Issues Cable barrier maintenance can be divided into two areas: repairs after crashes and on-going maintenance. Since cable barriers are used primarily in medians of heavily traveled highways, they tend to get hit quite often. For example, the first high-tension cable barrier installed in the United States on the Lake Hefner Parkway in Oklahoma has been hit over 500 times in 7 years of operation, which is an average of approximately 10 hits per mile per year over the 7-mile-long installation [24]. Therefore, cost of repair can be a major component of the life-cycle cost of cable barriers. Repairs after Crashes All current cable barriers have “weak” posts that are sacrificed in a crash and must subsequently be replaced. These posts are typically driven in soil, placed in sockets embedded in concrete foundations, or placed in driven sockets. Damaged driven posts may require special equipment for replacement. Socketed posts, on the other hand, can usually be replaced without specialized equipment, which reduces the repair cost. Post extraction problems can occur during subfreezing weather because the posts are often frozen in their sockets. Extraction problems also can occur when posts are sheared off at ground level rather than being bent over.

Literature review 19 Low-tension cable barrier systems lose their effectiveness after a crash because of the lack of tension in the cables, which causes the cables to droop, or even lie, on the ground. On the other hand, high-tension systems maintain their effectiveness after crashes as long as the anchors remain in place and a limited number of posts is destroyed. Figure 2.7a shows a low-tension 3-cable barrier after five posts were destroyed in a crash. Figure 2.7b shows a high-tension 3-cable barrier after four posts were destroyed in a crash. The number of posts damaged in a crash varies depending on the crash conditions. For high- tension systems most states report an average around seven posts that have to be replaced after a crash. Table 2.11 presents data on post replacements from seven states. Highway agencies report that repair times for high-tension systems typically range from 30 minutes to 2 hours except for crashes involving long sections of barrier. Arkansas recorded the repair time and cost for each crash that occurred during its first year of operation of the Brifen high-tension system. An average crash involved the replacement of 7.6 posts in 73 minutes at a cost of $302 [26]. Texas reported an average crash involved the replacement of 7.8 posts in 75 minutes [16]. Costs of repair reported by other states vary widely, partly depending on who does the repairs: DOT personnel or private contractors. Figure 2.7. Cable barrier systems after crash [25]. State No. of Crashes Ave No. Posts Damaged Ref Arkansas 44 7.6 [26] Arizona 104 8 [10] Colorado 19 4 [11] Indiana 6 [12] Iowa 4.2 [13] Oklahoma – Hefner PW 508 6.6 [27] Oklahoma – I-35 244 6.2 Texas – Brifen 65 6.6 [16]Texas – Trinity CASS 76 8.6 Texas – Nucor 6 9.5 Table 2.11. Average number of posts destroyed per crash—high-tension barriers.

20 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems On-Going Maintenance Most of the reported non-crash-related maintenance issues have involved soil conditions, post foundations, and/or anchors. Some barriers located along the median centerline have experienced problems with weak, saturated soils. The problems include anchor movement and post foundation failures. However, these same problems have been reported in higher areas where soils are not saturated. In many of these cases, the problem was due to an undersized anchor that was not able to resist the ambient tension in the cables. Figure 2.8 shows examples of anchor failures in Ohio and Texas. Figure 2.9 shows what happens when an anchor is destroyed in a crash. Anchors are critical to the performance of high-tension cable barriers, thus extra care needs to be taken to ensure that they are designed properly and located in areas least likely to be hit. Because of the large number of anchor failures, states are beginning to require greater monitoring of soil conditions and more detailed designs of anchors. Failure of concrete post foundations also has been a problem as shown in Figure 2.10. Lack of proper reinforcing steel and undersized designs for prevailing soil conditions appear to be the main causes for these failures. Frost heaving also could be associated with concrete footing failure in the northern states. All of the problems experienced with anchors and post foundations can be fixed by better engineering design, more carefully written specifications, and better oversight of construction. Another issue that was observed in the field is failure of connectors used at the barrier end-anchoring points. A study conducted by TTI investigated the strength of different types of connectors (termination fittings) used in cable barrier systems [65]. The objective of the study was to develop a more reliable connection that would reduce the likelihood of cable release during impacts. Different connector types were tested under static and dynamic loading conditions. The connectors included Filed Swage, Epoxy Socket, Precision Sure Lock (prototype 2), and Nucor Steel Marion terminations. In all tests, the cable did not pull out from the connector but rather ruptured. The maximum load varied from 140.0 to 177.8 kN (31.5 to 40.0 kips) under static loading and varied from 149.3 to 208.0 kN (33.6 to 46.8 kips) for the dynamic cases. The Figure 2.8. Examples of anchor failures in Ohio [28] and Texas [16].

Literature review 21 Figure 2.9. High-tension cable barrier after its anchor failure due to crash [28]. Figure 2.10. Examples of post foundation failures in Ohio [28].

22 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems researchers recommended the use of Field Swage as a retrofit for low-tension systems because it is easier to install than the Epoxy Socket and has higher maximum strength than the other terminations. The importance of proper installation was also emphasized in the study to ensure that full strength is reached and premature cable pull-out is avoided. In addition to static and dynamic testing, full-scale crash tests were conducted using the Epoxy Socket and Field Swage terminations. The tests showed that both terminations meet the NCHRP Report 350 TL3 rec- ommendation with the pickup truck test vehicle. It was noted, however, that due to its larger size in comparison to the Field Swage, the Epoxy Socket may affect the barrier performance when impacted with the small car test vehicle, therefore additional testing with this vehicle was recommended. 2.9 Review of Existing State DOT Guidelines As part of this project, information from highway agencies having their own cable barrier guidelines was solicited. Eight state DOTs responded (Arizona, Florida, Georgia, Kentucky, Louisiana, Minnesota, Mississippi, and Oklahoma). The majority of these states developed Special Provisions for use on individual projects using cable barriers, but Florida and Minnesota developed guidelines apparently intended to be incorporated as Standard Specifications. The following paragraphs summarize the content common to most of the existing guidelines and highlight the unique aspects contained in some of them. Although most of these states mandated the use of a 4-cable design tested and accepted as NCHRP Report 350 or MASH Test Level 4 (TL4) barriers, some accepted a 3-cable design at either TL3 or TL4. All states required that the line posts be set in sockets in concrete footings for ease of repair. Most specified a maximum allowed post spacing that ranged from 3 m (10 ft) to 5 m (16 ft). Again, most states specified post delineation (retro-reflective sheeting), ranging from 6 m (20 ft) along curves to 30 m (100 ft). An interval of about 15 m (50 ft) was most often specified. A site-specific soil analysis was required in the majority of states to ensure adequate end anchorage and post foundation designs. Florida DOT in particular included very detailed requirements in its Standard Specification for Tension Cable Barrier System. Minnesota’s Interim Design Guidelines for Tension Cable Guardrails was the only document received that included specific cable barrier design and layout information. Virtually all the state guidelines required that the cable barrier installers be trained or certified for this type of barrier and most required that training be given to state DOT personnel, particularly to maintenance forces charged with repairing or replacing crash-damaged hardware. A study undertaken by TTI attempted to formulate a comprehensive set of guidelines for the Texas DOT to provide for sound decision making for cable median barrier projects [29]. The recommendations are summarized in Table 2.12. They are categorized as guidelines for selection, design, placement, and general considerations. Commentary in the report provides the sources and the rationale for these guidelines. Much of the guidance is derived from current practices for other barriers, but the results of some of the analytic studies were incorporated. A study for the Kansas DOT by the Midwest Roadside Safety Facility (MwRSF) entitled “Cable Median Barrier Guidelines,” analyzed crash data to provide guidance for the determi- nation of where cable median barriers would be warranted [30]. This effort considered crash histories and the associated influencing factors, such as weather, terrain, and traffic, in the for- mulation of guidance. The benefit-cost ratios were computed for typical situations where cable barriers were considered an option. Due to local conditions, it was noted that the warranting conditions for Kansas (as other Midwest states) were different from those in the Roadside Design Guide.

Literature review 23 Area # Guidelines Selection 1 Utilize the recommended guidelines for installing me dian b arriers on h igh-speed roadways in Texas. 2 Cable barrier is for use only in roadway medians in Texas. 3 Cable barrier i s for use only o n me dians greater than 2 5 feet i n Texas. M edian widths o f 25 feet or less require the use of a mo re rigid barrier, such as a conc rete me dian barrier. 4 A 6:1 approach slope to the cable barrier syste m from both approach directions is required. 5 Roadway facilities with truck percentages of 10% or mo re should receive greater consideration for the use of TL4 cable barrier system s instead of TL3. 6 Cable barrier s ystems offer significant c ost savings over other m edian barrier s ystems such as Design 7 Four-cable syste ms should use an end-anchor term inal that provides for a separate anchor connection for cable or that has been crash-tested at the trailing end. 8 Post spacing for cable barrier syste ms should be specified when they are put out for bid. 9 A mi nim um clear distance of 12 feet s hould be ma intained from the edge of the cable barrier system. 10 The posts for all cable barrier syste ms should be placed in concrete drill shafts with sockets. 11 Use only prestretched cable. 12 13 Parallel runs of cable barrier may be a ppropriate for situations such as differential profile grades, narrow m edians, or when objects such as high-mast light poles are located i n the middle of the roadway median. 14 A mi nim um clear distance of 12 feet should be main tained between t he c able barrier system s, and any obstruction should be m aintained. 15 Cable barrier s ystems should be placed such t hat there is a minim um of 2.5 feet (6 feet preferred) from the back of the m etal beam guard fence posts to the barrier. 16 Cable barrier s ystems should be a mi nim um o f 6 feet behind g uardrail extruder terminals to allow for extrusion and gating of the end treatment. 17 Continue to m onitor overall cable barrier p erformance statewide, and evaluate im pacts from mo torcycles and vehicles exceeding design loads. Placement 18 As a general r ule, a cable barrier system s hould be placed as far away from the travel lane as possible while maintaining proper orientations and performance of the systems. 19 Cable barrier s ystems should be placed on relatively flat, unobstructed t errain if possible (10:1 or flatter) and ma y be placed on 6:1 maxim um slopes if necessary. 20 The preferred placem ent of the cable barrier within a v-ditch s hould not be in the area of 1 to 8 feet fro m the bottom of the ditch. 21 The acceptable place me nt of cable barrier allows a ma ximum 4:1 slope if the cable barrier is placed on the 6:1 slope at a distance of 8 to 1 feet from the ditch bottom . 22 Closer post spacing through horizontal curves is reco mme nded based upon t he r adius of curvature. 23 Place me nt of th e cable barrier on the convex side (i.e., inside of the curve relative to n ear traffic) is recommended to allow ma xi mu m median space for vehicle recovery for leaving opposing travel lanes. 24 Care should be exercised when placing cable barriers in superelevated sections. 25 Placement o f cable barrier systems on sag vertical alignments with a radius of less than a K - value of 11 should be avoided. 26 Cross drainage s tructures with l ess than 36 in ches of cover pose a challenge for placing cable barrier p osts. S tructures of l ess than 16 feet can be spanned in o rder t o avoid post p lacement into the drainage structure. 27 Designer should f ollow the Plans, Specifications and Estimates (PS&E) Preparation Manual General system considerations 28 Em ergency response agencies s hould have e ducational m aterials to p rovide t he m with c lear and concise guidance o n when a nd h ow t o safely cut cable when a vehicle is entangled after an im pact. 29 If th e cable barrier i s switched f ro m one m edian side to the other and term inals are not protected, o verlapping r uns of cable barrier a re recomm ended to p rovide a dequate protection from possible crossovers. 30 Footings for terminal anchors should b e designed to k eep s tatic loads well below the ultimate strength. 31 For future ma inten ance considerations, t he u se o f mo w strips is encouraged to reduce future hand m owing and herbicide operations. 32 Distance between the edge of the travel lane and the cable barrier should consider mo wer widths. 33 Anchor foundations a nd sockets should b e designed f or p revailing s oil conditions at installation locations. 34 Cable barrier system design should account for the potential of frost heave. 35 Delineation of cable barrier should be at 100 f oot spacing unless o therwise a pproved by the engineer. 36 The maxim um distance between breaks in the cable barrier s yste m that allow em ergency vehicle access should be 3 mi les. guidance on identifying utilities with the project and the quality level of utility locates required. concrete, which allows for installation of a greater number of miles for the same funding level. Cable barrier runs should be a minimum of 1,000 feet and a maximum of 10,000 feet in length. Table 2.12. Guidelines for the selection, design, placement, and use of cable median barriers recommended for Texas [29].

24 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems 2.10 International Practices The literature review included an attempt to determine the evolution of the technology and application of cable barriers in other parts of the world. These are summarized relative to use, evaluations, maintenance, and other concerns in the paragraphs below. Usage References were found to the use of safety fences, wire rope fences, and flexible barriers in Europe, Canada, Japan, Israel, Australia, and New Zealand. The use of modern cable barrier technology in some cases predates its use in the United States. A 1974 report entitled “Tensioned Cable Safety Barrier, M62,” by F. R. Oliver examined a trial installation of tension cable in the “central reserve” or median on the M62 motorway in England [31]. It was noted that the cable barriers’ smaller profiles nicely addressed the drifting snow problem that had been observed for median barrier applications. During the 2-year evaluation, 12 incidents occurred and were analyzed. It was noted that damage to vehicles was found to be relatively minor and, in most cases, the vehicles were driven away after the impact. The barrier also restrained a large truck. The author concluded that the experience of the trial suggests that the fears of injury to low sports cars and overriding by heavy vehicles are unfounded. The design of a TL4 cable median barrier for the Deerfoot Trail in Calgary was described in a 2007 paper [32]. This paper describes the preliminary engineering and design of an NCHRP Report 350 Test Level 4 high-tension cable barrier installed in the depressed median of an 11 km (6.8 mi) stretch of highway that had median side slopes of 6H:1V or flatter. At the time, three manufacturers met the NCHRP Report 350 requirements for four prestretched, post-tensioned cable barriers—namely, Brifen Canada, Gibraltar, and Trinity Highway Safety Products. The major design issues that were dealt with during the design and associated guidelines included • Lateral placement of median cable barrier – TL4 barriers can be installed in medians that have side slopes of 6H:1V or flatter. – On 6H:1V sloped medians, a cable barrier should be placed within 0.3 m (1 ft) of the ditch bottom or beyond 2.4 m (8 ft). – The ground under the barrier must be stable and free from obstructions or depressions. • Placement of the barrier – On a horizontal curve, the barriers were installed on the near side of the roadway, which is on the concave side of the barrier. • Connection to or separation from the existing barriers – At locations where existing barriers were in place, the median cable barrier was installed between the barrier and the travel lanes. • Existing hazards • Emergency crossovers – Crossovers were removed and the side slopes of the median graded to allow for continuous installation of the median cable barrier. • End treatments/terminals • Potential for vehicles to be trapped between barrier systems There was limited guidance for some of the design issues. Evaluation Various summaries of safety measures generated in the 1990s noted that wire rope systems had been promoted among the options for addressing safety problems. There were some small-scale

Literature review 25 evaluations of safety performance discovered, but nothing of a large scale. For example, Marsh and Pilgrim analyzed the performance of wire rope for the Centennial Highway in New Zealand [33]. A significant drop in the societal costs of crashes was noted for the 2+1 type application. The authors identified challenges for future installations of cable barriers in narrow medians. Levett, Job, and Tang compared the relative effectiveness of wide painted centerlines and wire rope systems on crossover occurrences and severity as part of a safe systems approach [34]. Candappa, D’Elia, and Newstead undertook a before and after study of flexible barriers along Victorian highways [35]. The study noted effectiveness of such barriers, particularly for reducing loss of control crashes. A 2004 study by McTiernan, Thoresen, and McDonald analyzed crash results and maintenance costs and found positive benefit-cost ratios when the Pacific Coast Highway installation was compared to other similar highways [36]. They recommended further application of modern wire rope barrier. Manuals and Guidance A document on cable barrier maintenance was generated in Western Australia. It identified conditions that need inspection during cable barrier system maintenance [37]. These included • Stretching of the rope • Movement of the anchors • Failure of the fittings • Release of the ropes from the anchors • Damaged posts or broken fixings • Lack of rope tension Wire rope and attachments are inspected for broken wire, reduction of wire diameter by abrasion, crushing or flattening of rope, kinking or notching, weakening by corrosion, damage to galvanizing, and any damage to the attachments and fittings. Actions to be taken when a defect is found included • Lubricate or replace a screw thread that is rusty or tight and • A competent person to decide whether to discard, or if possible, repair a damaged screw thread, distorted body, distorted fittings, nicks, gouges, cracks, or corrosion on any component Brifen Europe produced “Guidelines for the Installation, Inspection, Maintenance, and Repair of New and In-Service EN1317 Brifen Wire Rope Vehicle Restraint Systems (Europe)” [38]. This document sets out procedures for the installation and inspection of new and in-service Brifen wire rope safety fence systems. It presents various design requirements such as setback at verge, setback at central reserve, working width, number of ropes and tension factors for different containment levels, ground profile, height and length of fence, requirements on post foundation and anchors, and maximum length of ropes. It also lists various limitations on the use of wire rope fence. The document gives the guidelines for installing a Brifen wire rope fence including post selection, concrete foundations, filter drain foundations, anchors (end and intermediate), assembly, tensioning, and measuring tension in ropes. The document also explains the inspection program and the procedure for adding existing Brifen wire rope system to it. Various steps involved in maintenance of a Brifen wire rope system are explained in brief. These include mounting height, setback, working width, rope tension after impacts, component replacement, and various repairs after an impact. Woof noted in 2006 that although new barriers, like wire rope systems, were being developed, there are inadequacies in the testing requirements [39]. Nilsson and Prior described the decision process used by New South Wales to implement wire rope barriers in 2004 [40]. Roper et al.

26 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems noted that there were changes made in the 1987 AustRoads “Safety Barriers” guide that include flexible systems incorporating wire ropes [41]. Cable barriers in Japan are mainly used in snowy locations and scenic locations [42]. The main reasons for using cable barriers include easiness to remove snow from the roads and highways, unrestricted visibility, and that it is more economical when compared to other types of guardrails. Because of usual limited space for cable deflection, strong type posts are used to reduce barrier deflection. The number of cables and tension per cable varies depending on where the system is installed: roadside or median, highway, freeway, or local road. Cable size is common and is 18 mm (0.71 in.) in diameter. Tension per cable is 20 kN (4.3 kips) if installed on roadside in a freeway, otherwise it is 9.8 kN (2.1 kips). The number of cables varies from three to five depend- ing on the location of installation. Table 2.13 shows the various configurations of cable barriers. Applications In Sweden, the use of cable barriers for 2+1 applications on two-lane roads is reported as a means to improve safety. Carlsson and Larsson in 2003 (“Sweden Vision Zero Experience”) reported on the early experience of this application. Data from test sections showed that in eight incidents there were no fatalities and only six severe injuries [43]. This represented a 60 per- cent decrease in severe injuries compared to similar roads without the 2+1 design. They also noted that cable median barriers, although frequently hit, were normally occurring without personal injuries. A Swedish National Road Administration (SNRA) report indicated that the 2+1 roads were a “success story” [44]. In the 1990s almost 100 people were killed and more than 400 were severely injured on 13 m (43 ft) wide two-lane roads in Sweden. Seventy percent of these fatalities were due to vehicle run-offs and head-on accidents. SNRA started to explore cost-effective measures to improve traffic safety. The main alternative was the 2+1 concept, i.e., with central overtaking lane changing permitted every 1.25 km (0.78 mi) with a separating cable barrier preferably within the existing width of 13 m (43 ft). The results from this alternative design were compared with two other designs: 2+2 concept (i.e., to widen existing 13 m [43 ft] roads to two lanes in each direction separated with a cable barrier with a paved width of 16 m [52 ft]) and four-lane concept (i.e., with full access control and 18 m [59 ft] crown width including a 2.5 m [8.2 ft] median). The main results and findings until mid 2004 are as follows: • Safety effects for 2+1 concept are better than expected. Fatality rate reduced to 0.0017 (fatalities per million axle pair km), an 80 percent reduction. Reduction in severe injuries was about 55 percent. The 2+2 and 4-lane concepts provided not much better results than 2+1 concept. • Median cable crashes were, as expected, very frequent but normally without severe consequences. This rate is 0.51 crashes per million axle pair km. • Maintenance costs have increased by 70 percent, 65 percent of this being for barrier repairs. • Two fatalities and seven severe injuries have been reported involving motorcycles and cable barriers. No indication that the barrier created the accident or worsened the consequence. • Drivers and public opinion are very positive. Type Section Road Class Post Diameter Cable Diameter (# of Cables) Tension per Cable C Roadside Local road 114.3 mm 18 mm (3) 9.8 kN B Roadside Highway 114.3 mm 18 mm (4) 9.8 kN A Roadside Freeway 139.8 mm 18 mm (5) 20 kN Bm Median Highway 114.3 mm 18 mm (3) 9.8 kN Table 2.13. Japan’s various configurations of cable barriers.

Literature review 27 Other Concerns Schermans and Van der Hoek indicated that the 2+1 concept was being considered for the Netherlands. They noted that there are more motorcyclists in the Netherlands than in Sweden, which may cause a problem [45]. The opposition was already labeling cable barrier systems as “egg cutters.” Concerns raised by motorcyclists over the use of wire rope safety barriers (WRSB) included their potential to act as a “cheese cutter” in the event of a collision by a motorcyclist. Transit New Zealand generated a report to provide general guidance on the use of WRSBs with respect to the needs of motorcyclists [46]. The State Highway Geometric Design Manual, which is based on NCHRP Report 350 and AS/NZS 3845:1999 Road Safety Barrier Systems, provides guidance on the placement and layout of road safety barriers for both roadside and median barrier systems. The guide specifically states that unprotected road users, which includes motorcyclists, pedal cyclists, and pedestrians, should be taken into consideration. Crash data involving motor- cyclists in New Zealand between 2001 and 2005 shows that only a third of all motorcycle crashes occurred on the state highway network, whereas 70 percent of the fatal crashes that occurred were on these roads. Of the total 3,762 injury crashes involving motorcycles, 54 (1.4 percent) involved collision with a road safety barrier and 2 involved WRSB, but none of the motorcycle fatalities involved WRSB. The two crashes with WRSB resulted in the police reporting one serious injury and one minor injury. Several tests have been carried out on various types of barriers to assess the severity of injuries to the motorcyclists. Regardless of the various tests carried out, as noted in the 2006 ACEM Guidelines for PTW (Powered Two Wheelers)—Safer Road Design in Europe, “limited research done so far does not warrant the conclusion that cable barriers are more hazardous than other types of barrier” [47]. The report concludes that there is no reliable evidence to indicate that the wire rope barriers present greater or lesser risk than other barrier types, or indeed, no barrier at all [46]. The lack of evidence is due to the limited amount of accurate real world or microsimulation testing, along with the limited number of reported crashes involving motorcyclists and WRSBs. It also concludes that, depending on the use and positioning of WRSBs, they may result in a worse crash than if they had otherwise not been provided. Hence, care is required when specifying the need for road safety barriers, as well as when determining the type and location of such measures. A coroner’s report of an investigation of motorcycle death in Australia after crashing the motor cycle into high-tension cable barrier highlights concerns [48]. The cable barrier system was from Brifen and was installed in accordance with Australian Standards AS/NZS 3845:1999 Road Safety Barrier Systems. The location of the fence was site specific, meaning that it could not be positioned in any other location due to the steep drop on the other side. If the fence had been positioned part way down the embankment, an out-of-control vehicle would more likely travel over the fence. The only way to change the position of the fence would be if major road work was undertaken to change the configuration of the central median strip. From the investigation, it was concluded that the reasons for the death were that the person riding the motorcycle had a blood alcohol level more than three times the legal limit and was going at or about double the 110 km/h (62 mph) posted speed limit. Investigators did not believe that the cable barrier fence was to blame for the motorcycle rider’s death. Szwed presented a summary of the experience with wire rope barriers in Victoria [49]. He concluded based upon 10 years of deployment, a literature review, and a before and after crash analysis, that wire rope barriers are generally the safest type of barriers, and they are very cost- effective.

28 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems 2.11 Summary The literature review covered a broad spectrum of information sources and provided a viable snapshot of the current state of the practice. From the literature review, it is possible to conclude the following: • Cable barriers have a long history of use on highways. Improved designs for cable barrier systems have emerged over the past 10 years. • There is increasing use of cable median barriers across the country. • There is a general consensus that cable barrier systems have a high degree of effectiveness and lower crash severity when hit. • Although the generic low-tension systems are still an option for some, there seems to be a greater interest in high-tension cable systems. • Five companies are marketing proprietary cable barrier systems. The new cable barrier systems they are marketing vary considerably in their design features. • The new generation of cable barrier systems has been crash-tested to ascertain that they meet the requirements of NCHRP Report 350 or MASH. In assessing the performance of these barrier tests, it is important to note which criteria were used, because there is a difference in testing requirements between NCHRP Report 350 and MASH. • Efforts to evaluate the safety performance of cable barrier systems have not been uniform. The data, until recently, were not detailed enough to ascertain whether cross-median events actually resulted in crashes. • Differences in the data from the states, abilities to effectively isolate cross-median crashes, and limited data about site features resulted in a range of effectiveness estimates. • There only has been limited effort to analytically or physically evaluate the effectiveness of cable barrier systems to reflect the manner in which they are being used. • Placement of cable barriers has generally followed the accepted guidance for other barriers. There have been more tendencies to deploy cable barrier on sloped medians, but without analyses or test results to confirm effectiveness. The influences of median configuration, width, and slopes began under some research of the FHWA. • The heights, number, and arrangement of cables for any barrier system design vary. There is limited data to understand the influences of these cable factors on effectiveness. • The use of vehicle dynamics analysis (VDA) to assess vehicle-to-barrier interface has been shown to explain the occurrence of override and underride events. VDA tools provide a convenient means to consider the potential for bi-directional impacts of the barrier. • Issues with cable barrier anchorage failures have led to requirements for site-specific design anchorages. There has been some analysis of the effects of varying lengths of cable barriers. There are practices for setting the tension levels in cable barrier systems. • The relatively limited experience with cable barrier system deployments and maintenance over time implies that there is little data on initial and maintenance costs to provide clear guidance for selecting systems and ancillary features (e.g., mow strips, socketed posts). • Guidance is needed for determining where cable median barriers should be deployed, which systems should be selected, the needed design features, and their ultimate maintenance. The literature noted that there is only limited guidance of this nature and even where there is some guidance, like the Roadside Design Guide, it is dated, limited, and not specifically derived to reflect the features and functionality of cable barrier systems. • Most of the reported efforts are related to median applications, but these results are transferable to roadside applications. • The international literature noted uses of cable barriers or wire rope safety fences has occurred across the world. In some cases, the use of modern cable barrier technologies predates its use in the United States by more than 10 years.

Literature review 29 • The few evaluations of systems deployed in other parts of the world generally have concluded that wire rope systems have been effective in reducing the number and severity of crossover crashes. They have been judged to be “cost effective.” • The success with median applications has inspired the use of cable barriers in other applications. Most notably, in Sweden, Australia, and New Zealand, applications on 2+1 roads with narrow medians have been reported with good results. • There seems to be limited formal guidance or guidelines developed in other countries, and differences in basic road design practices render these guidelines of limited value to U.S. needs.